Daniel C. Josephson

Littoral Fish Community Response to Smallmouth Bass Removal from an Adirondack Lake

Large-scale observational studies in eastern Canada and the northeastern USA have concluded that introduced littoral predators are responsible for reductions in native fish diversity and abundance. To determine whether nonnative predator removal could increase native littoral fish abundance, we removed 47,682 smallmouth bass Micropterus dolomieu from a 271-ha Adirondack lake during a 6-year period. Two years after removal began, habitat-stratified snorkel surveys indicated a greater than 90% reduction in smallmouth bass abundance. The relative abundances of six native littoral species increased (4-90 times preremoval abundances) within 2 years of smallmouth bass removal. Decreased relative predation risk during the experiment reflected the reduction in littoral predators and identified seasonal differences in nearshore predation risk. The smallmouth bass population was resilient to removal, producing strong year-classes throughout the experiment. Mechanical removal was successful at decreasing smallmouth bass abundance and increasing native fish abundance, but removal must be conducted on a yearly basis to maintain low smallmouth bass population abundance. Our results provide experimental evidence regarding the need to prevent littoral predator introductions in Adirondack waters and offer support for nonnative control wherever native fish species conservation is a management priority.

Influence of Variable Interannual Summer Water Temperatures on Brook Trout Growth, Consumption, Reproduction, and Mortality in an Unstratified Adirondack Lake

Abstract Stressful water temperatures negatively affect physiological processes in fishes, yet evidence for how elevated temperatures influence population-level characteristics is rare. An 8-year field study of brook trout Salvelinus fontinalis in an unstratified Adirondack lake revealed that an aggregate measure of chronically stressful summer water temperatures strongly influenced brook trout population-level characteristics. We quantified chronic thermal stress using the cumulative degree-days over which bottom temperatures exceeded a range of thresholds (18–22°C) and found that the strongest relationships were with cumulative degree-days over 20°C (DD>20). Across years with similar brook trout densities, warmer summer water temperatures resulted in decreased brook trout growth, but growth was not reduced in a year with high water temperatures and low density. Maximum stomach fullness was negatively related to water temperature. Reproductive activity was negatively correlated with stressful summer ther...

Growth, Mortality, and Mark Retention of Hatchery Brook Trout Marked with Visible Implant Tags, Jaw Tags, and Adipose Fin Clips

Abstract Growth, mortality, mark retention, and mark readability were compared among control and treatment groups of 197–265-mm hatchery brook trout Salvelinus fonitinalis marked with visible implant (VI) tags, adipose tin (AD) clips, or stainless steel circularstrap jaw tags. Based on growth rates calculated for individual fish after 90 d, brook trout marked with VI tags grew faster than those with jaw tags (P G 0.03). Mortality was higher after 251 d for jaw-tagged fish (45%) than the cumulative mortality (8.3%) observed among VI-tagged, AD clipped, and control fish, Mark retention was 759c for VI tags, 99% for jaw tags, and 100% for AD clips, Visible implant tag loss was greatest within 7 d after insertion. After 251 d. 37% of the VI tags were unreadable. but 92% of the “unreadable” tags were readable if magnification and light were used. Unreadability could limit the usefulness of VI tags in multiyear studies unless problem tags can be removed from the fish to read tag codes.

Long-Term Retention and Visibility of Visible Implant Elastomer Tags in Brook Trout

Understanding how juvenile brook trout Salvelinus fontinalis from different sources contribute to fishable populations would be facilitated by a batch mark that could be applied to early life stages and be retained and visible throughout a fishs life. We evaluated visible implant elastomer (VIE) as a long-term batch mark for juvenile brook trout in hatchery and lake environments. Visible implant elastomer material was injected into the postocular eye tissue of 2,350 age-0 brook trout. Marked fish were stocked into three lakes, and an additional group was held in the hatchery. Tissue dissections revealed that VIE tag retention was 100% in both environments after 970 d. Tag visibility in hatchery fish examined under indoor fluorescent light was greater than 95% through 585 d, then dropped to 55-70% between 700 and 900 d. Tag visibility in lake fish examined under outdoor sunlight was 50-72% at 400 d and 0% at 959 d. When these same fish were observed in dark conditions with blue-filtered light and amber glasses, tag visibility was 75% for hatchery fish at 970 d and 100% for lake fish at 959 d. The high retention and increased visibility when viewed in dark conditions with blue-filtered light demonstrates that VIE tags are a suitable long-term batch mark for juvenile brook trout.

Growth, Movement, and Catch of Brook, Rainbow, and Brown Trout after Stocking into a Large, Marginally Suitable Adirondack River

Abstract Poststocking growth, movement, and catch were compared among hatchery brook trout Salvelinus fontinalis, rainbow trout Oncorhynchus mykiss, and brown trout Salmo trutta in a fifth-order river. Associations of species, size, and stocking date with angler catch were also examined. The river is episodically acidified, and during summer it approaches lethal maximum temperatures for trout. Catchable-sized brook and rainbow trout (168–458 mm total length) were stocked in the late spring of 1996 and 1997. Brown trout were stocked only in 1997. Fish were marked with visible implant tags and were recovered through October of each year. All three species had negative daily growth rates in weight over the summer and early fall. Rainbow trout stocked in 1997 tended to move downstream after stocking, whereas the other groups showed no strong movement trend. Recovery rates significantly differed between brook and brown trouts stocked in early June and those fish stocked in late May. Large (>300-mm) rainbow tro...

Comparison of large and small visible implant tags: retention and readability in hatchery brook trout.

Abstract Retention and readability of small (2.5 × 1.0 × 0.1-mm) and large (3.0 × 1.5 × 0.1-mm) visible implant (VI) tags were compared among different size-classes (211–470 mm total length, TL) of hatchery brook trout Salvelinus fontinalis. Among smaller size-groups (<400 mm TL), retention of large tags (63–86%) 100 d after tagging was less than retention of small tags (89–97%). Overall retention of large tags was much better among larger size-groups (≥400 mm TL) than among smaller sizes (97% versus 74%). Insufficient postorbital adipose tissue in smaller size-groups probably caused the poor retention of large VI tags. Retention was different between the two workers who inserted large VI tags. Readability of large and small tags was not affected by fish size at tagging. We recommend that large VI tags be used to mark brook trout longer than 400 mm TL because they are retained better. Fish with small tags from a previous study were subsequently monitored (and reported here) to assess retention and readabi...

Diet and prey selection of naturalized smallmouth bass in an oligotrophic Adirondack lake.

ABSTRACT Smallmouth bass (Micropterus dolomieu) introduced nearly 50 years ago have established a permanent population in Little Moose Lake, NY. Over 500 smallmouth bass were collected by angling in the littoral zone from June to August. Gut contents were compared for differences based on length of bass, date of capture, and substrate type where each fish was caught. Crayfish were the most frequent diet item and made up the largest percent composition by number. The average number of crayfish per stomach increased with bass length as did the number of fish per stomach. Crayfish, Ephemeroptera, Odonata, and fish made up 77% of the total number of diet items, excluding zooplankton. A noticeable diet shift from smaller diet items (Ephemeroptera) to larger ones (crayfish and fish) occurred when smallmouth bass approached 150 mm. A high amount of diet overlap occurred between bass caught over different substrate types and among most size classes. Smallmouth bass in Little Moose Lake were opportunistic feeders, using benthic, terrestrial, and pelagic littoral zone food resources. The most likely processes by which smallmouth bass affect salmonid and native fishes in Little Moose Lake are competition for food resources and predation.

Differences in Incubation Period and Survival of Embryos among Brook Trout Strains

Abstract The incubation period and survival of brook trout Salvelinus fontinalis embryos were compared among four genetically different strains: Temiscamie (Quebec), Assinica (Quebec), Horn Lake (Adirondack), and Little Tupper Lake (Adirondack). Eggs were fertilized and then incubated under cold (mean, 5.1°C) and warm (mean, 9.4°C) thermal regimes, and the accumulated degree-days and days to 100% hatch were recorded. Within all strains, embryos incubated under the warm thermal regime accumulated more degree-days to 100% hatch than embryos incubated under the cold regime. Degree-days to hatch differed between the two thermal regimes, ranging from 457 to 672 (P < 0.001). Mean degree-days to hatch also differed among strains (P < 0.001). Under the cold regime, Assinica strain embryos developed the fastest and hatched after the fewest degree-days (457), whereas Temiscamie strain embryos developed the slowest (549 degree-days). The two Adirondack strains developed at similar rates (Horn Lake, 486 degree-days; ...

Acidic Groundwater Discharge and in Situ Egg Survival in Redds of Lake-Spawning Brook Trout

Abstract Spawning of brook trout Salvelinus fontinalis in lakes occurs over areas of groundwater discharge. The rate and chemistry of groundwater discharge influence brook trout egg survival and reproductive success. While most studies have reported that groundwater discharge in brook trout redds is buffered relative to the surrounding lake water, we documented brook trout spawning over an area of acidic groundwater discharge (pH as low as 4.7) in a lake with circumneutral surface waters (pH > 6.1). A follow-up experiment that assessed in situ egg survival indicated 0% survival in redds with either low-pH groundwater or adequate groundwater pH but low groundwater discharge. More than 80% of eggs survived in a reference lake with well-buffered groundwater and adequate discharge rates. These results suggest that both low pH and low groundwater flow rates may contribute to brook trout egg mortality. Low-pH groundwater may be a factor to consider in brook trout restoration efforts, especially in lakes where w...

Summer Habitat Use by Introduced Smallmouth Bass in an Oligotrophic Adirondack Lake

ABSTRACT Non-native smallmouth bass became established in 1951 in Little Moose Lake, an oligotrophic Adirondack lake. Salmonids dominated the littoral zone at the time. Snorkel surveys, from late June through early August 1997, were used to determine the distribution and abundance of fish in the littoral zone. Transects were established on four habitat types: sand, wood (submerged trees), rock covered by silt (particles < 2 mm), and clean cobble (particles >64 mm). Non-native smallmouth bass were the most common fish species observed over the transects. Counts of adult smallmouth bass (Micropterus dolomieu) were greater than pumpkinseed (Lepomis gibbosus) and salmonids. Average lengths of bass were different between habitat types indicating size class segregation among the habitats in the littoral zone. Adult bass (>50 mm) were only observed on wood and cobble habitats. Nearly all bass >300 mm were observed on wood habitats. Young-of-year bass (<50 mm) were only observed on sand and silted rock. Only two brook trout (Salvelinus fontinalis) and three rainbow trout (Oncorhynchus mykiss) were observed; however, water temperature (range 21 °C to 24 °C) may have limited their presence. We conclude that non-native smallmouth bass dominate the littoral zone of this Adirondack lake during the summer.